It still goes back to carelessness. To me, there is a huge difference between a snap cap and a loaded round. Before I ever used a snap cap, I used once fired empties to drop the hammers on my doubles. I never had any trouble telling the difference between an empty and an unfired shell. Of course, I had also beaten the entire rims of .22 brass to death by using empties for dry firing revolver practice. I never managed to mix a loaded round in with the empties, but if I had, habit would have dictated that the muzzle was pointed in a safe direction when I pulled the trigger. I understand that accidents happen. But it's up to us to reduce them to as near zero as possible. That requires us to always maintain the same level of awareness as if we were near a spinning prop or saw blade. Owning and using guns is an awesome responsibility. I've always started with any new shooter by using water filled milk jugs, over-ripe melons, or the like, to show them the destructive force of even a puny .22 lr. I want them to understand that if they ever screw up and shoot a hunting companion or even themselves, someone could easily die. Even if we weren't brought up that way, we ought to retrain ourselves and make safe gun handling job #1 with any new shooter before they make a mistake with huge consequences.
I used to always think it was pretty cool to go into dozens of gun shows, each containing hundreds or thousands of firearms, and yet I felt as safe as safe could be. I'd think, if guns are so dangerous, this ought to be the worst place I could be on the planet. Yet there was never a problem. Never that is until about ten years ago when a vendor screwed up and bounced a 9m/m round off the floor of the Monroeville Expo Mart PGCA Gun Show and hit a patron in the leg. He thought the gun was unloaded. He obviously didn't take 2 seconds to check. And he pointed the gun inside a crowded building, put his finger on the trigger, and he pulled it. That wasn't a single mistake. That was four or five screw ups that led to an AD. I wasn't there that day, but that one incident caused enough unease that the whole venue changed and the show is now a shadow of what it once was.